1. Field of the Invention
The invention is directed to an improved electromechanical brake for motor vehicles.
2. Description of the Prior Art
A brake of this kind has been disclosed (WO 96/03301) in which an electric drive motor cooperates with a planetary roller screw drive whose spindle, depending on the supply of power to the motor, presses brake linings against a brake disc in an application stroke or moves these brake linings from contact with the brake disc in a restoring stroke. The position of the spindle is monitored by a sensor in order to limit the restoring stroke with a defined spindle position. Nevertheless, in the event of sensor failure, malfunctions in the control electronics of the brake, or even in the event of an incorrect electrical connection of the drive motor, when the spindle is being restored, the known brake does not prevent the permissible restoring stroke from being exceeded, does not prevent the planetary roller screw drive, for example, from becoming jammed or destroyed by the spindle striking against an obstacle, and does not prevent the motor from being overloaded.
In an electromechanical brake of this generic type known from U.S. Pat. No. 4,804,073, on the other hand, a clutch is provided, which in a first switched position in an application stroke of the brake, transmits the rotational movement of a drive motor to a screw link actuator, which is used to press brake linings against a friction element. When a permissible restoring stroke of the brake is achieved and exceeded, the clutch--in a second switched position--disengages the drive motor from the screw link actuator. A damage to the brake is thereby largely prevented. The clutch of the known brake is in fact embodied as very simple in structure, but since the function of the clutch is based on frictional engagement, its switching behavior can be subject to fluctuations, for example due to wear or due to the penetration of foreign matter.